Exhaust system for vehicle

ABSTRACT

An exhaust system for a vehicle having a combustion engine includes an elongate exhaust tube having a first end for receiving exhaust gases and a second end wherefrom the exhaust gases are emitted. An air cavity is tapered from its first end to its second end to increase a velocity of the flow of air as it passes in operation through the air cavity. The second end of the air cavity is disposed, in a direction of forward travel of the vehicle The flow of air from the second end of the air cavity interacts with the exhaust gases which are emitted from the elongate exhaust tube for causing a pressure reduction at the second end of the elongate exhaust tube. The exhaust system is capable, in operation, of providing an engine fuel efficiency improvement in a range of 7% to 23%.

TECHNICAL FIELD

The present disclosure relates generally to vehicles, and more particularly to an exhaust system for a vehicle.

BACKGROUND

Numbers of vehicles on roads around the World has increased considerably in past years. Atypically vehicle employs a gasoline or a diesel engine for generating motive power for propelling the vehicle. However, fuel consumption of the vehicles has been become an area of concern, especially in view of gradual depletion of fossil fuel reserves, so-called “peak oil”.

Generally, all engines are functionally associated with intake, compression, power and exhaust strokes or phases. For a given engine, during the exhaust stroke, a piston moves from a bottom dead centre (BDC) to a top dead centre (TDC) to force exhaust gases and/or vapour from an engine cylinder of the given engine through an exhaust port. Typically, although the given engine operates continuously; for example, during the exhaust stroke, momentum of a crankshaft and a flywheel of the given engine assist in pushing the exhaust gases out of the cylinder. However, a piston associated with the cylinder is still subjected to an additional load or pressure, generally imposed by the exhaust gases and vapour, during the exhaust stroke. This additional load slows down the movement of the piston when it pushes the exhaust gases and vapours from the cylinder, requiring additional effort from the given engine, which may increase the fuel consumption of the given engine.

Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks associated with the fuel consumption of the given engine, mutatis mutandis its associated vehicle.

SUMMARY

The present disclosure seeks to provide an exhaust system for a vehicle.

The present disclosure also seeks to provide a method of improving fuel efficiency of a vehicle.

In one aspect, an embodiment of the present disclosure provides an exhaust system for a vehicle including a combustion engine, characterized in that the exhaust system includes:

an elongate exhaust tube having a first end for receiving exhaust gases from the combustion engine, and a second end wherefrom the exhaust gases are emitted; an air cavity having a first end for receiving a flow of air, and a second end for exhausting the flow of air, wherein the air cavity is tapered from its first end to its second end to increase a velocity of the flow of air as it passes in operation through the air cavity, and wherein the second end of the air cavity is disposed in operation in a range of 20 mm to 250 mm in front, in a direction of forward travel of the vehicle, of a leading edge of the second end of the elongate exhaust tube; and an interaction zone whereat the flow of air from the second end of the air cavity interacts with the exhaust gases which are emitted from the second end of the elongate exhaust tube for causing a pressure reduction at the second end of the elongate exhaust tube caused by gaseous viscous drag of the air flow, wherein a plane of the second end of the elongate exhaust tube subtends an angle α relative to a plane which is substantially parallel to an elongate axis of the interaction zone, and wherein the angle α is in a range of 10° to 60°.

Such an arrangement is of advantage in that the pressure reduction is capable of more efficiently exhausting exhaust gases from the engine.

In another aspect, an embodiment of the present disclosure provides a method of improving fuel efficiency of a vehicle including a combustion engine, characterized in that the method includes:

(i) arranging for the vehicle to include an elongate exhaust tube having a first end for receiving exhaust gases from the combustion engine, and a second end wherefrom the exhaust gases are emitted; (ii) arranging for the vehicle to include an air cavity having a first end for receiving a flow of air, and a second end for exhausting the flow of air, wherein the air cavity is tapered from its first end to its second end to increase a velocity of the flow of air as it passes in operation through the air cavity, and wherein the second end of the air cavity to be disposed in operation in a range of 20 mm to 250 mm in front, in a direction of forward travel of the vehicle, of a leading edge of the second end of the elongate exhaust tube; and (iii) arranging, in operation of the vehicle, for there to be an interaction zone whereat the flow of air from the second end of the air cavity interacts with the exhaust gases which are emitted from the second end of the elongate exhaust tube for causing a pressure reduction at the second end of the elongate exhaust tube caused by gaseous viscous drag of the air flow, wherein a plane of the second end of the elongate exhaust tube to subtend an angle α relative to a plane which is substantially parallel to an elongate axis of the interaction zone, wherein the angle α is in a range of 10° to 60°.

In an example, the elongate exhaust tube has a cavity between its first end and its second end, wherein the cavity has a transverse diameter which is greater than that of the first and second ends of the elongate exhaust tube.

Optionally, the elongate exhaust tube is, in operation, downwardly curved, upwardly curved or sideways curved towards its second end.

In an example, the air cavity is operable to generate the air flow in response to vehicle being propelled in a forward direction by the combustion engine.

Optionally, the air cavity has a cross-section area which reduces from its first end to its second end by a ratio of one of at least 1:5, at least 1:10, and at least 1:20.

Optionally, the air cavity has a length, in a direction of forward travel of the vehicle, in a range of 200 to 600 mm.

In an example, a lower edge of the second end of the air cavity is less than 5 mm below a lower edge of the second end of the elongate exhaust tube.

Optionally, the second end of the elongate exhaust tube has a diameter in a range of 40 mm to 90 mm.

More optionally, in that the air cavity:

(i) at its first end, has a first edge dimension in a range of 50 mm to 120 mm in a first edge direction, and its first end has a second edge dimension in a range of 250 mm to 400 mm in a second edge direction, wherein the first and second edge directions are substantially mutually orthogonal; and (ii) at its second end, has a first edge dimension in a range of 20 mm to 40 mm, in a first edge direction, and its second end has a second edge dimension exceeding a dimension of the second end of the elongate exhaust tube by about 15 mm to 20 mm in a second edge direction, wherein the first and second edge directions are substantially mutually orthogonal.

Optionally, the second end of the elongate exhaust tube has an elliptical or circular cross-section.

More optionally, the air cavity is implemented as a plastics-material structure and/or a sheet metal structure.

In an example, at least a part of the exhaust system is designed to be retrofitted to a pre-existing exhaust arrangement of the vehicle.

Optionally, the exhaust system is arranged to be used in conjunction with the combustion engine being of gasoline and/or diesel type. However, it will be appreciated that the exhaust system can also be used in relation to vehicles with engines that utilize for fuel at least one of: LPG, methane, methanol, ethanol, Hydrogen.

Embodiments of the present disclosure substantially eliminate, or at least partially address the aforementioned problems in the background, and provide improved fuel efficiency for a vehicle. Specifically, the system and the method of the present disclosure enable a reduction to be achieved in an additional load or pressure generally imposed on a piston (when moving from BDC to TDC) by the exhaust gases and vapour during an exhaust stroke. For example, the exhaust system of the present disclosure is configured to create a reduced pressure zone at an exit point of an exhaust arrangement with the help of gaseous viscous drag of an air flow. This helps in reducing an additional effort (which causes power losses or more fuel consumption) required by an engine to overcome the additional load or pressure imposed on the piston during the exhaust stroke, and thereby increasing the fuel efficiency for the vehicle.

Additional aspects, advantages, features and objects of the present disclosure would be made apparent from the drawings and the detailed description of the illustrative embodiments construed in conjunction with the appended claims that follow.

It will be appreciated that features of the present disclosure are susceptible to being combined in various combinations without departing from the scope of the present disclosure as defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the present disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those in the art will understand that the drawings are not to scale. Wherever possible, like elements have been indicated by identical numbers.

Embodiments of the present disclosure will now be described, by way of example only, with reference to the following diagrams wherein:

FIG. 1 is a schematic illustration of an exhaust system for a vehicle, in accordance with an embodiment of the present disclosure;

FIG. 2 is schematic illustration of an air cavity of the exhaust system of FIG. 1, in accordance with an embodiment of the present disclosure;

FIG. 3 is a schematic illustration of a vehicle arranged with of the exhaust system of FIG. 1, in accordance with an embodiment of the present disclosure;

FIG. 4 is a schematic illustration of an exhaust system for the vehicle, in accordance with a different embodiment than the present disclosure; and

FIG. 5 is an illustration of steps of a method of improving fuel efficiency of a vehicle having a combustion engine, in accordance with an embodiment of the present disclosure.

In the accompanying drawings, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing.

DETAILED DESCRIPTION

The following detailed description illustrates embodiments of the present disclosure and ways in which they can be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognize that other embodiments for carrying out or practicing the present disclosure are also possible.

It should be noted that the terms “first”, “second”, and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Further, the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

Referring now to the drawings, particularly by their reference numbers, FIG. 1 is a schematic illustration an exhaust system 100, in accordance with an embodiment of the present disclosure. The exhaust system 100 is functionally associated with a combustion engine of a vehicle. The vehicle primarily relates to a roadable vehicle, such as car, van, truck and the like. Alternatively, the vehicle can be a waterbody vehicle, such as boat or ship, having a combustion engine. In an embodiment, the combustion engine can be one of a gasoline or a diesel type, although other types of engine are alternatively employed, for example LPG engine. Moreover, the combustion engine can be one of a two-stroke or a four-stroke combustion engine.

As shown, the exhaust system 100 includes an elongate exhaust tube 102, an air cavity 104 and an interaction zone 106. The elongate exhaust tube 102, the air cavity 104 and the interaction zone 106 are hollow structures integrally coupled to each other. In an embodiment, the air cavity 104 is coupled to an intermediate or a central portion of the elongate exhaust tube 102. Moreover, the interaction zone 106 encloses an end portion of each of the elongate exhaust tube 102 and the air cavity 104, which is explained in greater detail herein later.

The elongate exhaust tube 102 includes a first end 110 and a second end 112. The elongate exhaust tube 102 also includes a cavity 114 between the first end 110 and its second end 112. In an embodiment, the cavity 114 includes a transverse diameter which is greater than that of the first and second ends 110, 112 of the elongate exhaust tube 102. Specifically, the elongate exhaust tube 102 includes a central portion 116, between the first and second ends 110, 112, having a larger diameter compared to the diameters of the first and second ends 110, 112.

In an embodiment, the elongate exhaust tube 102 is, in operation, downwardly curved, upwardly curved or sideways curved towards its second end 112. In the present embodiment, as shown in FIG. 1, the second end 112 of the elongate exhaust tube 102 is downwardly curved. Moreover, the second end 112 of the elongate exhaust tube 102 includes a diameter in a range of 40 mm (millimeter) to 90 mm, more optionally substantially 60 mm. Furthermore, the second end 112 of the elongate exhaust tube 102 includes an elliptical or circular cross-section. For example, the second end 112 can either have a circular cross-section having a diameter of 60 mm, or have an elliptical cross-section having a major axis of 60 mm. In an embodiment, the first end 110 of the elongate exhaust tube 102 may also include a similar structural configuration that of the second end 112, i.e. a circular or elliptical cross-section having a diameter or a major axis of about 60 mm.

Further, the air cavity 104 is an elongate hollow structure having a first end 120 and a second end 122. The air cavity 104 is tapered from its first end 120 to its second end 122. Specifically, the air cavity 104 includes a cross-section area which reduces from its first end 120 to its second end 122. In an embodiment, the cross-section area of the air cavity 104 from the first end 120 to its second end 122 reduces by a ratio of at least 1:5, more optionally at least 1:10, and most optionally substantially 1:20, as shown in FIG. 2.

Referring now to FIG. 2, there is provided a schematic illustration of the air cavity 104, in accordance with an embodiment of the present disclosure. As shown, the air cavity 104 at its first end 120 includes a first edge 202, having a dimension in a range of 50 mm to 120 mm, in a first edge direction A. The air cavity 104 at its first end 120 also includes a second edge 204, having a dimension in a range of 250 mm to 400 mm, in a second edge direction B. Moreover, the first and second edge directions A, B are substantially mutually orthogonal. The first end 120 also includes a third edge 206 and a fourth edge 208, opposite and parallel to the first and second edges 202, 204, respectively, and also includes similar dimensions that of the first and second edges 202, 204.

The air cavity 104, at its second end 122, includes a first edge 212 having a dimension in a range of 20 mm to 40 mm, more optionally substantially 30 mm, in a first edge direction C. The air cavity 104 at its second end 122 also includes a second edge 214, having a dimension exceeding a dimension (i.e. the diameter in a range of 40 mm to 90 mm) of the second end 112 of the elongate exhaust tube 102 by about 15 mm to 20 mm, in a second edge direction D. Moreover, the first and second edge directions C, D are substantially mutually orthogonal. Additionally, the second end 122 includes a third and a fourth edge (not shown) opposite and parallel to the first and second edges 212, 214, respectively, and includes similar dimensions that of the first and second edges 212, 214. The air cavity 104 also includes a length L, distance between the first and second ends 120, 122, in a range of 200 to 600 mm.

Referring back to FIG. 1, the interaction zone 106 is an elongate hollow structure, which encloses at least a portion of each of the second ends 112, 122 of the elongate exhaust tube 102 and the air cavity 104, respectively. Moreover, the second ends 112, 122 are spaced apart from each other. The second end 122 of the air cavity 104 is disposed in operation in a range of 20 mm to 250 mm in front, in a direction X of forward travel of the vehicle, of a leading edge 118 of the second end 112 of the elongate exhaust tube 102. The distance (i.e. in the range of 20 mm to 250 mm) between the second end 122 and the leading edge 118 of the second end 112 is represented by D1.

Further, as shown, a plane P1 of the second end 112 of the elongate exhaust tube 102 subtends an angle α relative to a plane P2 which is substantially parallel to an elongate axis E of the interaction zone 106. The angle α is in a range of 10° to 60°, more optionally substantially 30°. Moreover, a lower edge 124 of the second end 122 of the air cavity 104 is less than 5 mm below a lower edge (such the leading edge 118) of the second end 112 of the elongate exhaust tube 102. The distance (of about 0-5 mm) between the lower edge 124 of the air cavity 104 and the lower edge of the elongate exhaust tube 102 is represented by D2. Further, the first edge 212, of the air cavity 104, at its second end 122 is configured to have a dimension such that 124 lies in P2 but not more than 5 mm below. In an example, the lower edge 124 of the second end 122 can lie in the plane P2 (i.e. when D2=0).

Additionally, a trailing edge 119 of the second end 112 is spaced apart from a second end 130 of the interaction zone 106 by a distance D3, for example of about 150 mm. Also, the trailing edge 119 of the second end 112 lies 3 mm to 5 mm inside the wall of the interaction zone 106.

In an embodiment, the exhaust system 100 may be made of a heat resistant material. For example, the elongate exhaust tube 102, the air cavity 104 and the interaction zone 106 may be made of metallic sheets. Otherwise, the exhaust system 100 may also include a non-metallic component. For example, the air cavity 104 may be implemented as a plastics-material structure.

Referring now to FIG. 3, there is provided a schematic illustration of a vehicle 300 arranged with the exhaust system 100 of FIG. 1, in accordance with an embodiment of the present disclosure. Specifically, at least a part of the exhaust system 100 is designed to be retrofitted to a pre-existing exhaust arrangement of the vehicle 300. For example, as shown, the exhaust system 100 may be coupled or retrofitted to a tail pipe 302 of the pre-existing exhaust arrangement. For example, the first end 110 of the elongate exhaust tube 102 may be detachably coupled to the tail pipe 302 using metallic clamps. Alternatively, the first end 110 may be integrally coupled to the tail pipe 302 using welding.

In operation, the first end 110 of the elongate exhaust tube 102 is configured to receive exhaust gases (and/or vapours) from a combustion engine (not shown), and the second end 112 of the elongate exhaust tube 102 wherefrom the exhaust gases are emitted (shown with arrows Y). Moreover, the first end 120 of the air cavity 104 receives a flow of air (shown with arrows Z), and the second end 122 of the air cavity 104 exhausts the flow of air. Therefore, the air cavity 104 is operable to generate the air flow (shown with arrows Z) in response to the vehicle 300 being propelled in a forward direction X by the combustion engine.

Further, as mentioned above, the air cavity 104 is tapered from its first end 120 to its second end 122 to increase a velocity of the flow of air as it passes in operation through the air cavity 104. Therefore, in the interaction zone 106 whereat the flow of air from the second end 122 of the air cavity 104, interacts with the exhaust gases which are emitted from the second end 112 of the elongate exhaust tube 102, causes a pressure reduction at the second end 112 of the elongate exhaust tube 102 due to gaseous viscous drag of the air flow. The pressure reduction accordingly helps in reducing a power required to overcome an additional load or pressure generally imposed on a piston (inside a cylinder) by the exhaust gases and/or vapour during an exhaust stroke of the combustion engine. Specifically, the reduced pressure in the interaction zone 106 helps in pulling out the exhaust gases and/or vapour from the second end 112 of the elongate exhaust tube 102. This reduces effort or fuel consumption during the exhaust stroke of the combustion engine, which in turn improves the fuel efficiency of the vehicle 300.

In an embodiment, an exhaust system, such as the exhaust system 100 of the present disclosure, may include following dimensions, i.e.

-   -   D1 250 mm     -   D2 0     -   L 520 mm     -   208 240 mm     -   202 100 mm     -   212 30 mm     -   214 80 mm     -   α 35     -   D3 150 mm     -   106 oval cross-section having a major axis of 100 mm         Further, the exhaust system with above dimensions may be         conveniently used in conjunction with a specific car model, such         as Peugeot 1.6 litre diesel engine.

Below is a chart depicting data associated with the increased fuel efficiency for various vehicles, with the application of an exhaust system, such as the exhaust system having above dimensions. The chart lists down vehicles specification and driving conditions. Also, the chart lists down values of fuel consumption with and without the exhaust system.

Vehicles specification & Fuel utilization Fuel utilization Driving conditions without Exhaust with Exhaust (hp = horsepower) system system Peugeot (Peugeot is a registered trademark) 5.3 litres/100 km 4.2 litres/100 km 1.6 litre capacity diesel engine, 115 hp; Ran mostly on roads Peugeot 2.2 litre capacity diesel engine, 204 hp; 6.5 litres/100 km 5.0 litres/100 km Ran mostly on motorways at 130 km/h Peugeot 1.6 litre capacity gasoline (turbo) 8.5 litres/100 km 7.0 to 7.5 litres/100 km engine, 200 hp; Ran mixed (road and motorway) Suzuki (Suzuki is a registered trademark) 1.3 6.5 litres/100 km 5.5 litres/100 km litre capacity gasoline engine, 92 hp; Ran on measured motorway at 110 km/h Suzuki 1.3 litre capacity gasoline engine, 92 hp 7.5 litres/100 km 7.0 litres/100 km Ran mixed (road and motorway) Chevrolet (Chevrolet is a registered trademark) 11 litres/100 km 8.5 litres/100 km 3.4 litre capacity gasoline engine, 210 hp; Ran on measured motorway at 110 km/h, Peugeot 2 litre capacity gasoline (turbo) 9.5 to 10 8.0 to 8.5 litres/ engine, 160 hp; litres/100 km 100 km Ran most on highway/motorway Based on the above chart, the use of exhaust system in conjunction with vehicles substantially increases the fuel efficiency thereof. For example, use of exhaust system may increase the fuel efficiency (depending on vehicles specifications and driving conditions) in a range of 7% to 23%, for example substantially 10%. As aforementioned, the air flow provided via the air cavity is generated by forward movement of the vehicle through air, such that the air cavity “scoops up” air and then increases its flow velocity by way of a generally tapered construction which is utilized for the air cavity. Thus, the air flow is provided “passively” by way of forward motion of the vehicle, as aforementioned. Optionally, the air flow is additionally fan-assisted, namely is provided “actively”, for example by employing a radial fan and/or centrifugal fan. Optionally, the fan is utilized selectively, for example only when the vehicle is travelling at low forward speeds, for example at forward speeds of less than 25 km/hour.

Referring now to FIG. 4, illustrated is an exhaust system 400 for a vehicle (such as the vehicle 300), in accordance with a different embodiment than the present disclosure. As shown, the exhaust system 400 also includes an elongate exhaust tube 402, an air cavity 404, and an interaction zone 406. However, the structural configuration of the exhaust system 400 differs from the structural configuration the exhaust system 100 of FIG. 1. For example, a second end 412 of the elongate exhaust tube 402 includes a straight configuration (instead of downwardly curved second end 112 of the elongate exhaust tube 102). Moreover, the air cavity 404 is coupled to the interaction zone 406 (instead of being coupled to the central portion 116 of the elongate exhaust tube 102), such that second ends 412, 422 of the elongate exhaust tube 402 and the air cavity 404, respectively, are substantially enclosed by the interaction zone 406. Optionally, in FIG. 1 and FIG. 4, the air flow provided via the air cavity 404, is fan-assisted, for example from a cooling fan (not shown) of the engine of the vehicle 300.

Referring now to FIG. 5, illustrated are steps of a method 500 of improving fuel efficiency of a vehicle having a combustion engine, in accordance with an embodiment of the present disclosure. Specifically, the method 500 is associated with utilization of an exhaust system, such as the exhaust systems 100, in conjunction with the vehicle, such the vehicle 300, for improving a fuel efficiency of the vehicle.

At step 502, a vehicle is arranged to include an elongate exhaust tube (such as the elongate exhaust tube 102 of FIG. 1) having a first end for receiving exhaust gases from the combustion engine and a second end wherefrom the exhaust gases are emitted. For example, the elongate exhaust tube may be coupled to a tail pipe of the of a pre-existing exhaust arrangement for receiving the exhaust gases from the combustion engine. Further, the elongate exhaust tube to have a cavity between its first end and its second end, and the cavity has a transverse diameter which is greater than that of the first and second ends of the elongate exhaust tube.

At step 504, the vehicle is arranged to include an air cavity (such as the air cavity 104 of FIG. 1) having a first end for receiving a flow of air and a second end for exhausting the flow of air. The air cavity is tapered from its first end to its second end to increase a velocity of the flow of air as it passes in operation through the air cavity. Further, the second end of the air cavity to be disposed in operation in a range of 20 mm to 250 mm in front, in a direction of forward travel of the vehicle, of a leading edge of the second end of the elongate exhaust tube, and a lower edge of the second end of the air cavity to be less than substantially 5 mm below a lower edge of the second end of the elongate exhaust tube.

At step 506, the vehicle is arranged, in operation, for there to be an interaction zone (such as the interaction zone 106 of FIG. 1) whereat the flow of air from the second end of the air cavity interacts with the exhaust gases which are emitted from the elongate exhaust tube for causing a pressure reduction at the second end of the elongate exhaust tube caused by gaseous viscous drag of the air flow. Further, a plane of the second end of the elongate exhaust tube to subtend an angle α relative to a plane which is substantially parallel to an elongate axis of the interaction zone, the angle α is in a range of 10° to 60°. As aforementioned, the reduction in pressure inside the interaction zone helps in pulling out the exhaust gases from the second end of the elongate exhaust tube. This reduces effort or fuel consumption during an exhaust stroke of a combustion engine, thereby improving fuel efficiency of the vehicle.

It will be appreciated that the method 500 is also associated with configuration or arrangement of the exhaust system, such as the exhaust system 100, on the vehicle. For example, the method 500 further relates to the structural and functional aspects of the elongate exhaust tube, the air cavity and the interaction zone to constitute the exhaust system, which is explained in detail in conjunction with FIGS. 1 to 3. Therefore, description thereof is avoided for the sake of repetition and brevity.

Modifications to embodiments of the invention described in the foregoing are possible without departing from the scope of the invention as defined by the accompanying claims. Expressions such as “including”, “comprising”, “incorporating”, “consisting of”, “have”, “is” used to describe and claim the present invention are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. Numerals included within parentheses in the accompanying claims are intended to assist understanding of the claims and should not be construed in any way to limit subject matter claimed by these claims. 

1. An exhaust system for a vehicle including a combustion engine, wherein the exhaust system includes: an elongate exhaust tube having a first end for receiving exhaust gases from the combustion engine, and a second end wherefrom the exhaust gases are emitted, an air cavity having a first end for receiving a flow of air, and a second end for exhausting the flow of air, wherein the air cavity is tapered from its first end to its second end to increase a velocity of the flow of air as it passes in operation through the air cavity, and wherein the second end of the air cavity is disposed in operation in a range of 20 mm to 250 mm in front, in a direction of forward travel of the vehicle, of a leading edge of the second end of the elongate exhaust tube; and an interaction zone whereat the flow of air from the second end of the air cavity internets with the exhaust gases which are emitted from the second end of the elongate exhaust tube for causing a pressure reduction at the second end of the elongate exhaust tube caused by gaseous viscous drag of the air flow, wherein a plane of the second end of the elongate exhaust tube subtends an angle α relative to a plane which is substantially parallel to an elongate axis of the interaction zone, and wherein the angle α is in a range of 10° to 60°.
 2. An exhaust system as claimed in claim 1, wherein the elongate exhaust tube has a cavity between its first end and its second end, wherein the cavity has a transverse diameter which is greater than that of the first and second ends of the elongate exhaust tube.
 3. An exhaust system as claimed in claim 1, wherein the elongate exhaust tube is, in operation, downwardly curved, upwardly curved or sideways curved towards its second end.
 4. An exhaust system as claimed in claim 1, wherein the air cavity is operable to generate the air flow in response to vehicle being propelled in a forward direction by the combustion engine.
 5. An exhaust system as claimed in claim 1, wherein the air cavity has a cross-section area which reduces from its first end to its second end by a ratio of one of at least 1:5, at least 1:10, and at least
 120. 6. An exhaust system as claimed in claim 1, wherein the air cavity has a length, in a direction of forward travel of the vehicle, in a range of 200 mm to 600 mm.
 7. An exhaust system as claimed in claim 1, wherein a lower edge of the second end of the air cavity is less than 5 mm below a lower edge of the second end of the elongate exhaust tube.
 8. An exhaust system as claimed in claim 1, wherein that the second end of the elongate exhaust tube has a diameter in a range of 40 mm to 90 mm.
 9. An exhaust system as claimed in claim 1, wherein the air cavity: (i) at its first end, has a first edge dimension in a range of 50 mm to 120 mm in a first edge direction, and its first end has a second edge dimension in a range of 250 mm to 400 mm in a second edge direction, wherein the first and second edge directions are substantially mutually orthogonal; and (ii) at its second end, has a first edge dimension in a range of 20 mm to 40 mm, in a first edge direction, and its second end has a second edge dimension exceeding a dimension of the second end of the elongate exhaust tube by about 15-20 mm in a second edge direction, wherein the first and second edge directions are substantially mutually orthogonal.
 10. An exhaust system as claimed in claim 1, wherein that the second end of the elongate exhaust tube has an elliptical or circular cross-section.
 11. An exhaust system as claimed in claim 1, wherein that the air cavity is implemented as a plastics-material structure and/or a sheet metal structure.
 12. An exhaust system as claimed in claim 1, wherein at least a part of the exhaust system is designed to be retrofitted to a pre-existing exhaust arrangement of the vehicle.
 13. An exhaust system as claimed in claim 1, wherein the exhaust system is arranged to be used in conjunction with the combustion engine being of gasoline and/or diesel type.
 14. A method of improving fuel efficiency of a vehicle including a combustion engine, wherein the method includes: (i) arranging for the vehicle to include an elongate exhaust tube having a first end for receiving exhaust gases from the combustion engine, and a second end wherefrom the exhaust gases are emitted; (ii) arranging for the vehicle to include an air cavity having a first end for receiving a flow of air, and a second end for exhausting the flow of air, wherein the air cavity is tapered from its first end to its second end to increase a velocity of the flow of air as it passes in operation through the air cavity, and wherein the second end of the air cavity to be disposed in operation in a range of 20 nun to 250 nun in front, in a direction of forward travel of the vehicle, of a leading edge of the second end of the elongate exhaust tube; and (iii) arranging, in operation of the vehicle, for there to be an interaction zone whereat the flow of air from the second end of the air cavity internets with the exhaust gases which are emitted from the second end of the elongate exhaust tube for causing a pressure reduction at the second end of the elongate exhaust tube caused by gaseous viscous drag of the air flow, wherein a plane of the second end of the elongate exhaust tube to subtend an angle α relative to a plane which is substantially parallel to an elongate axis of the interaction zone, wherein the angle α is in a range of 10° to 60°.
 15. A method as claimed in claim 14, wherein the method includes arranging for the elongate exhaust tube to have a cavity between its first end and its second end, wherein the cavity has a transverse diameter which is greater than that of the first and second ends of the elongate exhaust tube.
 16. A method as claimed in claim 14, wherein the method includes arranging for the elongate exhaust tube to be, in operation, downwardly curved, upwardly curved or sideways curved towards its second end.
 17. A method as claimed in claim 14, wherein the method includes arranging for the air cavity to be operable to generate the air flow in response to vehicle being propelled in a forward direction by the combustion engine.
 18. A method as claimed in claim 14, wherein that the method includes arranging for the air cavity to have a cross-section area which reduces from its first end to its second end by a ratio of one of at least 1:5, at least 1:10, and at least 1:20.
 19. A method as claimed in claim 14, wherein the method includes arranging for the air cavity to have a length, in a direction of forward travel of the vehicle, in a range of 200 mm to 600 mm.
 20. A method as claimed in claim 14, wherein the method includes arranging for a lower edge of the second end of the air cavity to be less than substantially 5 mm below a lower edge of the second end of the elongate exhaust tube.
 21. A method as claimed in claim 14, wherein that the method includes arranging for the second end of the elongate exhaust tube to have a diameter in a range of 40 mm to 90 mm.
 22. A method as claimed in claim 14, wherein that the method includes arranging for the air cavity: (i) at its first end, to have a first edge dimension in a range of 50 mm to 120 mm in a first edge direction, and its first end to have a second edge dimension in a range of 250 mm to 400 mm in a second edge direction, wherein the first and second edge directions are substantially mutually orthogonal; and (ii) at its second end, to have a first edge dimension in a range of 20 mm to 40 mm, in a first edge direction, and its second end to have a second edge dimension exceeding a dimension of the second end of the elongate exhaust tube by about 15-20 mm in a second edge direction, wherein the first and second edge directions are substantially mutually orthogonal.
 23. A method as claimed in claim 14, wherein the method includes arranging for the second end of the elongate exhaust tube to have an elliptical or circular cross-section.
 24. A method as claimed in claim 14, wherein the method includes arranging for the air cavity to be implemented as a plastics-material structure and/or a sheet metal structure.
 25. A method as claimed in claim 14, wherein that the method includes arranging for at least a part of the exhaust system to be designed to be retrofitted to a pre-existing exhaust arrangement of the vehicle.
 26. A method as claimed in claim 14, wherein the method includes arranging for the exhaust system to be used in conjunction with the combustion engine being of gasoline and/or diesel type. 